Ultraviolet (UV), which is contained in sunlight, is a light having wavelengths that are shorter than wavelengths of visible light that human being can sense. Components of UV, which can reach to the surface of the earth, are classified into UV-A having wavelengths of 320 to 400 nm (long wavelength UV) and UV-B having wave lengths of 290 to 320 nm (medium wavelength UV). Radiation of such UV causes deteriorations of industrial products such as a breaking of plastic materials, discoloration of paints and the like, as well as causing unignorable damages to human skins.
On the other hand, the concepts for emphasizing the environmental protection and the safety are propagating throughout the world, and applied researches for utilizing biomass, which is typical environmental cycling process, are actively conducted. Lignin is a nature biomass, which, as well as cellulose and hemicellulose, constitutes a plant, and constitutes about 20 to 35% of a lumber. A number of herbaceous plants also include lignin. Lignin provides improved physical strength to the plant cell walls, as well as serving functions for preventing degradations by living substances and/or serving functions for controlling flowability of water by providing hydrophobicity to cell walls. Lignin is an irregular polymer, which has parahydroxyphenyl propane as its basic skeleton and is created by dehydrogenative polymerization of a monolignol having 0 to 2 methoxyl group(s), namely p-coumaryl alcohol, coniferyl alcohol or sinapyl alcohol.
The use of such lignin as a raw material of a UV absorber is examined (Patent Literature 1, Non-Patent Literature 1).
Patent Literature 1 describes that a lignin, which is separated and extracted from a plant material by utilizing microwave and microwave-sensitized catalyst, is employed as a UV absorber.
Non-Patent Literature 1 discloses a report related to dimers contained in degradation product of lignin by CuO oxidation.